Department of Chemistry, University of North Carolina at Chapel Hill, Chapel Hill, North Carolina 27599, USA.
Nature. 2010 Jun 3;465(7298):598-601. doi: 10.1038/nature09085.
Chemical reactions inside single crystals are likely to be highly selective, but examples of single crystal to single crystal (SC-SC) transformations are uncommon, because crystallinity is difficult to retain following the rearrangement of atoms in the solid state. The most widely studied SC-SC transformations involve solvent exchange reactions in porous coordination polymers or metal-organic frameworks, which take advantage of the robust polymeric networks of the hosts. Examples of reactions occurring within molecular organic crystals generally involve photo-induced reactions, such as the coupling of alkenes or alkynes within the crystal. For nonporous molecular inorganic or organometallic crystals, single-crystal transformations involving the formation or cleavage of metal-ligand bonds are rare; known examples usually involve ligand loss from the single crystal and reversible religation, a process sometimes accompanied by decay of the single crystal to a microcrystalline powder. Here we report a series of SC-SC transformations that involve the interchange of multiple small gaseous ligands (N(2), CO, NH(3), C(2)H(4), H(2) and O(2)) at an iridium centre in molecular single crystals of a pincer Ir(I) complex. The single crystal remains intact during these ligand-exchange reactions, which occur within the crystal and do not require prior ligand extrusion. We reveal a selective catalytic transformation within a nonporous molecular crystal: pincer iridium single crystals ligated with nitrogen, ethylene or hydrogen show selective hydrogenation of ethylene relative to propylene (25:1) when surface sites are passified by CO.
在单晶体内的化学反应可能具有高度的选择性，但单晶到单晶（SC-SC）转变的例子并不常见，因为在固态下原子重新排列后很难保持结晶度。研究最广泛的 SC-SC 转变涉及多孔配位聚合物或金属有机骨架中的溶剂交换反应，这些反应利用了主体的坚固聚合物网络。在分子有机晶体中发生的反应的例子通常涉及光诱导反应，例如在晶体内部烯烃或炔烃的偶联。对于无孔分子无机或有机金属晶体，涉及形成或断裂金属-配体键的单晶转变很少见；已知的例子通常涉及从单晶中失去配体和可逆的重新配位，这一过程有时伴随着单晶衰减为微晶粉末。在这里，我们报道了一系列涉及在分子钳式 Ir(I)配合物的单晶中 Ir 中心处多个小气态配体（N(2)、CO、NH(3)、C(2)H(4)、H(2)和 O(2)）的交换的 SC-SC 转变。在这些配体交换反应中，单晶保持完整，这些反应在晶体内部发生，不需要预先挤出配体。我们揭示了非多孔分子晶体中的选择性催化转变：当 CO 使表面位点失活时，氮、乙烯或氢配位的钳式铱单晶对乙烯相对于丙烯（25:1）具有选择性加氢。
